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1730, hypothetical inflammatory principle, formerly believed to exist in all combustible matter, from Modern Latin (1702), from Greek phlogiston (1610s in this sense), neuter of phlogistos "burnt up, inflammable," from phlogizein "to set on fire, burn," from phlox (genitive phlogos) "flame, blaze" (see bleach (v.)). Theory propounded by Stahl (1702), denied by Lavoisier (1775), defended by Priestley but generally abandoned by 1800. Related: Phlogistic; phlogisticated.
A hypothetical colorless, odorless, weightless substance once believed to be the combustible part of all flammable substances and to be given off as flame during burning. In the 18th century, Antoine Lavoisier proved that phlogiston does not exist. See Note at Lavoisier.
in early chemical theory, hypothetical principle of fire, of which every combustible substance was in part composed. In this view, the phenomena of burning, now called oxidation, was caused by the liberation of phlogiston, with the dephlogisticated substance left as an ash or residue.